It has been well known for a number of years that saturated polymeric substances are modified when subjected to bombardment with high energy particulate radiation including accelerated charged particles such as electrons and protons and the particles emitted by nuclear fission. See, for example, U.S. Pat. No. 2,951,024. It has also been known that ethylenically unsaturated polymers may be irradiated with ultraviolet light to yield polyesters having improved properties such as increased tensile strength, and increased solvent resistance. See, for example, U.S. Pat. No. 3,496,839. Additionally, it is known to treat polymers with a combination of ultraviolet, visible, and infrared high intensity radiation to form polymer cross-links which result in improvements in many of the above-mentioned properties. See, for example, U.S. Pat. No. 3,650,699. It is further known that the use of low intensity ultraviolet radiation from mercury lamps to effect cross-linking of certain polymers (e.g., saturated non-halogenated polymers) requires extended periods of exposure and in some instances is completely ineffective. See U.S. Pat. No. 3,650,699. Excessive exposure of many of the cross-linkable polymers to this type of radiation source may result in discoloration, stiffness, lessened strength, broken fils, dullness, and ever charring. It is still further known to introduce cross-linking into polymers by adding cross-linking promoters to the polymers prior to their irradiation. See, for example, U.S. Pat. No. 2,961,389. It has also been generally observed that the efficiency of high energy particles in cross-linking polymers is quite low. See, for example, U.S. Pat. No. 2,961,389. Hence, relatively heavy irradiation doses, which are expensive to produce and time-consuming to apply, are required to obtain cross-linking of saturated polymers which in turn improves the solvent resistance of the compounds so cross-linked. Further, in many instances this form of radiation has a degradative effect on the material being treated. It has been further observed that those methods of inducing cross-linking of polymers which involve the use of promoters have the disadvantages of lengthy induction periods, and temperature variation during treatment.
The present invention is unique in that it discloses a method for enhancing solvent resistance of non-ethylenically unsaturated brominated or chlorinated fibrous polyester materials by exposing these compounds to low intensity and low energy ultraviolet radiation for extremely short periods of time.
Saturated polymers are difficult to cross-link because there is no position on the polymer where cross-linking can take place in the conventional manner associated with unsaturated polymers. In the presently claimed invention the halogenated positions of the saturated polymer provide a site for cross-linking upon exposure to ultraviolet radiation. Such exposure liberates radicals which in turn react with each other to form cross-linked structures.
Brominated and chlorinated aromatic polyesters have been used to produce a number of inherently non-burning fibrous materials which offer the public a great degree of fire safety, particularly when fibrous articles are required for use in fire-control environments, e.g., children's sleepwear, suits for fire fighters, hospital furnishings, uniforms for military and civilian flight personnel, etc. However, the fabrics made from these materials tend to dissolve, to at least some degree or to be otherwise adversely influenced, when contacted with hydrocarbons or conventional dry cleaning fluids such as tri-chloroethylene, perchloroethylene, tetrachloroethylene, tetrachloroethane, chloroform, carbon tetrachloride, methylene chloride, and Stoddard solvent.
It is therefore an object of this invention to provide a method for decreasing the solubility in conventional dry cleaning solvents of brominated or chlorinated non-ethylenically unsaturated aromatic polyester fibrous materials in less time and with lower energy requirements than have heretofore been required.
It is another object of this invention to provide a method for the treatment of solid preformed brominated or chlorinated aromatic polyester fibrous materials which enhances solvent resistance without a significant detrimental change in other product properties, such as, for example, discoloration to the exposed substrate.
It is still another object of the present invention to provide a substantially solvent resistant brominated or chlorinated aromatic polyester fibrous product which also possesses increased thermal dimensional stability, and increased water resistance.
These and other objects as well as the scope, nature and utilization of the invention will be apparent to those skilled in the art from the following description and appended claims.